(1) Field of the Invention
This invention relates to a novel anion-exchange membrane having improved performance. The anion-exchange membrane provided by this invention has the property of permitting selective permeation of anions having a low electric charge when used for electrodialyzing an aqueous solution containing various salts. Surprisingly, when an aqueous solution containing an acid and a salt or a neutral soluble compound is applied to it it also has the property of selectively permitting diffusion and permeation of the acid.
It is an object of this invention to provide a novel anion-exchange membrane having the aforesaid special properties, and a process for its production. The invention also provides a method of electro dialysis or diffusion dialysis using the above anion-exchange membrane as a dialysis diaphragm, above all for separation of an acid from an aqueous solution containing the acid and a salt or a neutral soluble compound (also meant to include a soluble high-molecular-weight compound).
(2) Description of the Prior Art
In Japan, much work has been done over many years on the imparting of permselectivity between ions of the same sign to ion-exchange membranes as one sector of the salt-making technology based on the concentration of sea water by electrodialysis, and such exchange membranes have already been utilized industrially. As regards the production of anion-permselective membranes, there have been proposed a method which comprises polycondensing a monomer on the surface of an anion exchange membrane to form a thin dense layer of a crosslinked structure (Japanese Patent Publication No. 15258/1961), a method which comprises oxidatively decomposing only the surface portion of a basic anion-exchange membrane (Japanese Patent Publication No. 34649/1965), a method which comprises forming another anionic thin layer on the surface of an anion-exchange membrane (Japanese Patent Publication No. 30693/1970), a method which comprises inactivating the surface portion of an anion exchange membrane (Japanese Patent Publications Nos. 34999/1973 and 1071/1978), and a method of producing an anion-exchange membrane by treatment with a Lewis acid to crosslink only the surface layer with haloalkyl groups (Japanese Patent Publication No. 8049/1981).